1. Field of the Invention
The present invention relates generally to an apparatus and method for retransmission in a wireless communication system, and in particular, to a retransmission apparatus and method for Mobile Stations (MSs) with fixedly allocated radio resources in the wireless communication system.
2. Description of the Related Art
In a wireless communication system, a Base Station (BS) allocates resources to Mobile Stations (MSs) for providing a service and then transmits resource allocation information to the MSs using a resource allocation message.
The wireless communication system communicates using limited time-frequency resources. Thus, the resource allocation message acts as an overhead in the wireless communication system. For example, when supporting a service that periodically generates traffic, such as a Voice of IP (VoIP) service, a BS periodically sends a resource allocation message including resource allocation information to MSs. If the BS periodically allocates the same resource to the MSs, the BS periodically sends the same resource allocation message to the MSs. Consequently, resources are unnecessarily wasted because the BS is periodically sending the same resource allocation message.
In order to solve this problem, a BS may allocate fixed radio resources to an MS performing a type of service that periodically generates traffic. Thereafter, the MS periodically performs communicates using radio resources initially fixedly allocated by the BS. Consequently, the BS reduces overhead for a resource allocation message because the BS is only sending the resource allocation message to the MS when initially allocating the fixed radio resources.
A wireless communication system also uses Automatic Retransmission reQuest (ARQ) to enhance the reliability of data transmission and increase a throughput.
For example, in a downlink, an MS identifies errors by decoding a received packet. If there is no error in the received packet, the MS sends an acknowledgement (ACK) message to a BS. If there is an error in the received packet, the MS sends a negative acknowledgement (NACK) message to the BS.
Upon receiving the ACK message from the MS, the BS transmits a new original packet. Upon receiving the NACK message, the BS retransmits a packet in response to the NACK message. Here, the BS distinguishes whether a transmitted packet is an original packet or a retransmission packet using a distinction factor included in a resource allocation message. The distinction factor includes an ARQ channel IDentification (ID), an ARQ ID sequence number, etc. That is, the MS identifies the kind of the received packet through the resource allocation message received from the BS.
When radio resources are fixedly allocated as described above, the BS of the wireless communication system does not send a resource allocation message except when initially allocating radio resources or changing fixedly allocated resources. Therefore, there is a problem that the MS cannot distinguish the kind of packet received from the BS, if the wireless communication system applies ARQ. Also, there is a problem that the MS cannot identify which original packet the retransmission packet is for, even though the MS may be able to identify a retransmission packet.